have you thought of removing the PWM heatsink and re-tim? this is a common problem with many motherboards, almost as a rule many will strip off any factory heatsinks on a board and re-tim them before using any board. i personally do as well, for some reason they seem to use some crappy tim, or have poor contact, or both. another issue might be warping (slight) of your board, which might cause some contact issues. be careful though! you wont want to much torque.

water is cool, i use full board blocks now personally. Since that is an overclocking board i would recommend it. I was walked through my first MB installation by a friend over videochat, which helps, there are many things to learn. WARNING: water can get expensive, fast!
some do question the necessity of motherboard blocks of course, but with the issues your having it will probably be warranted. you might try the re-tim first though.

how well is the air flowing into the case? if it isnt flowing in very well it of course will not flow out very well.